This invention relates to systems and methods for reproducing true or idealized signal waveforms despite the presence of inconstant and virtually unmeasurable deviations arising from internal components, and more particularly to systems and methods for reproducing sound with fidelity.
Modern electronic systems utilize a great number of compensation techniques for improving the linearity or sensitivity of a circuit, such as feedback circuits, passive networks and active networks. It is common practice to arrange discrete elements, or the equivalent in integrated circuit elements, so as to provide a desired compensation where the disturbing effect is measurable. Where the disturbing effect is not measurable but is somehow evidenced in the output, the solution has usually been to choose materials or components that exhibit the least disturbing effect under these conditions.
Applicants have worked extensively in the field of high fidelity sound reproduction, and in the elimination of spurious emanations in reproduced sound, as evidenced by U.S. Pat. No. 4,340,778 entitled "Acoustic Systems". Minimization of these spurious emanations has enabled identification of other disturbing factors, particularly with audio systems and components of good design. It became evident that numerous influences are at play in an audio system, and that these influences are inconstant in nature and are derived from internal operative factors that have heretofore been accepted as necessary limitations on performance, given the need for reasonable system economy. The inconstant deviations of sound are perceptible to the human ear because of the great capabilities and subtlety of that instrument, even though typical measuring instruments cannot quantify effects which are several orders of magnitude less than the dominant signal, and which vary dynamically in accordance with a complex multi-frequency wave.
Applicants first confronted this problem in terms of the disparity in performance between a magnetic phonograph cartridge of the moving magnet or moving iron type, in contrast to the substantially more expensive (and difficult to replace) moving coil type of phonograph cartridge. It was deduced that hysteresis effects in the magnetic circuit might be the cause of the inconstant perturbations, although of the many magnetic circuits and devices now in use there are no known suggestions for cancellation of hysteresis effects. Instead, the typical approach appears to have been to attempt to utilize materials having minimum hysteresis loss, where this has been recognized as a problem. Similarly, there has been recognition in the audio field that the quality of reproduced sound is recognizably affected by the nature of the input cable connection, but the primary solutions known have merely been to utilize higher cost cables with superior conductivity (e.g., better shielding and gold-plated contacts). Applicants have found, however, that there are a number of similar disturbing factors of what may be regarded as a hysteretic character, in that they are time variant in nature and signal amplitude dependent and are second order or high order effects that cannot be simulated by conventional compensating techniques. Elimination of such factors in a manner that does not significantly alter the price of a system enables a substantial increase in performance to be achieved, making a given system competitive with more expensive units without any fundamental system reconstruction or redesign.
The same phenomenon, of an inconstant hysteretic or other non-linear variation, is exhibited in a wide number of systems in which internal components can have a profound effect upon system performance. Just as variations which cannot be measured by practical means are discernible to the ear in a high fidelity audio system, so too do minute variations within a video display or reproducing system have a disturbing effect on image resolution or color fidelity. In addition, low noise signal detectors provide subtly distorted outputs because of internal functional deviations that cannot be compensated by conventional means.